Defects in CTSA, CTSD, CTSF, and CTSK result in galactosialidosis, neuronal ceroid lipofuscinoses (NCLs) type 10 and type 13, and pycnodysostosis, respectively [13,43,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149] (Table 2). The gene discussed is CTSK; the disease is pycnodysostosis.